Simple core body thermometers without heating (hereafter referred to as non-heating core body thermometers, refer to Patent Literatures 1 to 3) are used to measure the temperature of a core part of a body.
The basic principle for measuring (calculating) the core body temperature with a non-heating core body thermometer will now be described with reference to FIGS. 16A to 16C.
To measure the core body temperature with a non-heating core body thermometer, as shown in FIG. 16A, a heat flux sensor, which includes temperature sensors arranged separately on the upper and lower surfaces of a heat insulator having a relatively large area, is placed in tight contact with a body surface.
The thermal circuit shown in FIG. 16A can be expressed as an electric circuit in FIG. 16B, where Tb is the core body temperature, Ta is the temperature of the surface of the heat insulator exposed to the outside air, Tt is the temperature of the surface of the heat insulator in contact with the body surface, R1 is the thermal resistance of subcutaneous tissue as a non-heat generator, and R2 is the thermal resistance of the heat insulator.
When the temperature of each part of the heat flux sensor placed in tight contact with the body surface is stabilized, the quantity of heat passing through the non-heat generator per unit time is equal to the quantity of heat passing through the heat insulator per unit time. As a result, Formula 1 is derived.(Tb−Tt)/R1=(Tt−Ta)/R2  (1)
Thus, the core body temperature Tb can be calculated using Formula 2 below.Tb=Tt+(Tt−Ta)·R1/R2  (2)
The non-heating core body thermometer calculates the core body temperature Tb based on the above principle.